Thursday, March 06, 2008

Scientists have developed a computerised mind-reading technique which lets them accurately predict the images that people are looking at by using scanners to study brain activity.

The technique relies on functional magnetic resonance imaging (fMRI), a standard technique that creates images of brain activity based on changes in blood flow to different brain regions. The first step is to train the software decoder by scanning a subject's visual cortex while they view thousands of images over five hours. This teaches the decoder how that person's brain codes visual information. The next stage is to take a new set of images and use the decoder to predict the brain activity it would expect if the subject was viewing each of them. Finally, the subject views images from this second set while in the scanner. "We simply look through the list of predicted activities to see which one is most similar to the observed activity, and that's our guess," said Gallant.

The software matched their observed brain activity with the predicted activity from the decoder. When using a set of 120 images, the software got it right nine out of 10 times. With 1,000 images, the accuracy was eight out of 10. For 120 images, if the software were to simply make random predictions, its success rate would be just 0.8%.

The study raises the possibility in the future of the technology being harnessed to visualise scenes from a person's dreams or memory.

Writing in the journal Nature, the scientists, led by Dr Jack Gallant from the University of California at Berkeley, said: "Our results suggest that it may soon be possible to reconstruct a picture of a person's visual experience from measurements of brain activity alone. Imagine a general brain-reading device that could reconstruct a picture of a person's visual experience at any moment in time."